The use of heat-resistant, light-weight and brittle alloys (e.g. intermetallic phases), and also ceramic materials for rotor blades has generally failed due to the low impact strength of these materials and the attending high risk of catastrophic blade damage or failure as a result of foreign body ingestion into the turbine or of a blade fracture. The heat-resistant and high-alloy materials currently in use for rotor blades, such as nickel (Ni) or cobalt (Co) based alloys, do have an adequate impact strength, but unfortunately also have a relatively high specific weight. The resulting high total rotor weight causes great stresses in the disks of high speed turbines, such as low-pressure turbines. The high rim loads arising on the outer circumference of the disk rims result in a comparatively short useful life of the disks.
An additional problem is posed by the need to cope with the relatively high blade vibration excitation energies that arise, especially in view of the rotor blade strength needed for withstanding the centrifugal loads. Thus, vibration induced fatigue results in an increased risk of blade failure.
U.S. Pat. No. 2,772,854 (Anxionnaz) (issued Dec. 4, 1956) discloses a rotor of the above described general type, wherein the rotor blade airfoils are to be braced against one another to damp vibrations, when under sufficiently high centrifugal loads. For this purpose, the prior art rotor of the above cited patent includes tongue-shaped members projecting circumferentially from the two rotor blades of each pair. The two adjacent tongue-shaped members of each pair have different circumferential lengths and overlap one another axially and circumferentially at overlapping end portions, with a spacing gap or clearance formed between the overlapping ends. When the turbine operates at a prescribed speed, this clearance or spacing gap becomes zero due to the differing radial deflection of the different length tongue-shaped members. Thus, adjacent blades are braced or supported radially against one another, so that the respective blade vibration energy of each blade is dissipated through component friction of the overlapping end portions of the tongue-shaped members rubbing against one another.